I would leave the kegs off gas until you hit your target PSI/CO2 volume. You are currently over-pressured, so when you use the pressure relief valve, head space gas gets released, right. Well, some of that excess gas in solution will come out of solution and fill that head space (Law of partial pressure) until pressure in beer = pressure in head space. Then release gas via pressure relief valve, and rinse repeat until you're at the PSI you want. It sucks, I know. I'm only slightly more advanced in kegging than you, but science is science.